1. Field of the Invention
The invention relates to a method of distance estimation, more particularly to a method of distance estimation to be implemented using a digital camera.
2. Description of the Related Art
As shown in FIG. 1, in U.S. Pat. No. 4,263,719, there is disclosed an optical device for use as a gun sight, telescope or viewfinder and capable of indicating the distance of a target from the user. The optical device includes a reticule 1 with vertically displaced segmented horizontal lines 101 that are calibrated to give the viewer an instant indication of range of the target without requiring mechanical adjustment. Although the distance of the target from the viewer may be determined through the reticule 1, the segmented horizontal lines 101 have a very high requirement of manufacturing precision. Moreover, once manufactured, the design and specification of the reticule 1 cannot be altered. In other words, an optical device can only be installed with a reticule 1 having a specific design and specification.
FIG. 2 illustrates a conventional digital camera 2 that is capable of distance measurement and that includes a laser emitter 201 and a laser receiver 202. When laser light emitted from the laser emitter 201 is reflected back to the laser receiver 202 from a target (not shown), a digital signal processor (not shown) in the digital camera 2 is able to calculate the distance between the target and the viewer based on the time difference between laser light emitting and laser light receiving, wherein the distance is equal to one half of the product of the calculated time difference and the speed of light.
However, the need to provide the digital camera 2 with the laser emitter 201 and the laser receiver 202 not only increases the size of the digital camera 2, but also increases the manufacturing cost of the digital camera 2 significantly.